The present invention relates to a motor-driven blower for a vacuum cleaner, and a method of manufacturing an impeller for such a motor-driven blower.
An impeller included in a conventional motor-driven blower comprises a front plate provided in its central part with a suction opening, a back plate disposed opposite to the front plate, and blades disposed between the front and the back plate. Each of the blades is provided with projections to be deformed for securing the blades, the projections being inserted in slots formed in the front and the back plate, and the parts of the projections projecting from the front plate and the back plate are crushed to fix the blades to the front plate and the back plate. All of those components of the impeller are formed of an Al alloy. The impeller thus assembled is fastened to the rotatable shaft of a motor with a screw, and a fan casing is disposed over the impeller to form the motor-driven blower.
A motor-driven blower intended for use in a recent vacuum cleaner was designed so as to operate at an increased operating speed to produce an increased suction with an improved efficiency.
Since the impeller of the conventional motor-driven blower is constructed by crushing the parts of the projections projecting from the front plate and the back plate, as mentioned above, the crushed parts of the projections protrude from the outer surfaces of the front plate and the back plate. The resistance of air against the movement of the crushed parts of the impeller is significant when the impeller rotates at a high rotating speed and is an impediment to the possible increase of the operating speed of the motor-driven blower.
A technique proposed in, for example, JP-A No. 1-310198 to solve such a problem rounds the corners of end parts of the projections to be crushed to reduce the air resistance against the movement of the crushed parts of the projections.
Although the technique proposed in JP-A No. 1-310198 rounds the corners of end parts of the projections to be crushed to reduce air resistance against the movement of the crushed parts of the projections, the crushed parts still remain on the outer surfaces of the front plate and the back plate. Therefore, there is a limit to the reduction of the air resistance that can be achieved in this way and so the crushed parts remain as a significant impediment to an increase of the operating speed of the motor-driven blower.
An increase in the operating speed of the motor-driven blower entails an increase in stress induced in the impeller. Therefore, the rigidity of the impeller must be enhanced. Since the components of the conventional impeller are fastened together by crushing protruding parts of the blades and the strength of the joints of the components formed in this way is lower than the strength of the blades and the plates, the rigidity of the impeller constructed by assembling the components in this manner provided by the prior art is not very high, and hence increase in the rotating speed of the impeller is limited.
An increase in the operating speed of the motor-driven blower entails an increase in the load on the rotating shaft of the electric motor. Therefore, it is necessary to reduce the load on the rotating shaft of the electric motor by reducing the weight of the impeller, which is typically formed of an Al alloy.